This is an era of offbeat, hitherto-unheard-of case materials like forged carbon, tantalum, alusic, titanium ceramic and even something called “Texalium” (aluminum-coated carbon fiber). But one “new” case material has been around so long it has a prehistoric age named after it: bronze. In recent years, brands including IWC, Panerai, Zenith, Squale, U-Boat, Anonimo, Bulgari, Oris, Tudor and now Montblanc have introduced bronze watches. Most are divers’ watches or have a nautical theme; for them, bronze, used for centuries to make ship fittings and seafaring equipment, is a way to underline their maritime identity. In other watches, bronze is used simply for its appearance: the metal has a vintage-like matte patina, which differs from watch to watch and hence makes each watch unique. Here’s a look at this time-honored metal.
Alloys that contain at least 60 percent copper can be called “bronze,” but the term usually refers to alloys that are made from a mixture of copper and tin. Pure copper is relatively soft and dents easily while tin is brittle and breaks. But when combined, the resulting alloy resists wear, retains its shape and is antimagnetic. And its most outstanding property is its ability to resist corrosion in seawater.
Bronze is somewhat more brittle than stainless steel and weighs about 10 percent more. It reacts with oxygen, which results in a distinctive patina. This coating, which is oxidized copper, protects the underlying material against corrosion but leaves all other characteristics unchanged.
Among the various mixtures of copper and tin, experts distinguish between wrought or worked alloys, which include as much as 9 percent tin, and cast alloys, which usually contain between 9 and 12 percent tin. Bronzes that contain 20 percent tin are called “bell bronze.”
But bronzes are seldom made of just copper and tin; adding other materials creates alloys with tailor-made properties. Phosphorus and zinc are usually added to alloys that are wrought; these two substances as well as lead, nickel and iron are added to cast alloys. These blends are known as “multi-alloy bronzes.” If alloys contain little or no tin, they’re called “special bronzes.” The copper-aluminum blend used by the watch brand Anonimo is in this category. When a material other than tin is added to copper, the resulting alloy is named for the additional substance, i.e., “aluminum bronze,” “lead bronze,” “phosphorus bronze,” etc. Manufacturers use different alloys to create each brand’s distinctive nuances of color.
Aluminum bronze is a golden yellow alloy that can be cast and wrought. It usually contains between 9 and 14 percent aluminum. Iron, manganese and nickel are often added to aluminum bronze. Anonimo uses a type of aluminum bronze that contains 84 percent copper and 11.5 percent aluminum, in addition to smaller quantities of nickel, manganese, iron, zinc, tin and lead. A very thin exterior film of aluminum results in this alloy’s extremely high resistance to saltwater. Anonimo has used aluminum bronze since 1997. Each series that Anonimo offers includes at least one model with a bronze case.
Panerai relies on the bimetallic alloy CuSn8 for its bronze cases, which it has used for two limited-edition watches. CuSn8 contains 92 percent copper and 8 percent tin. Ickler, a case manufacturer based in Pforzheim, Germany, also uses this bronze alloy for the cases of its Archimede pilots’ watches. Archimede has three bronze-cased models in its standard collection.
The first of Panerai’s bronze limited editions debuted in 2011. The Luminor Submersible 1950 3 Days Automatic Bronzo has a sea-green dial to underline the brand’s history as a supplier of dive watches and other diving instruments. Panerai equipped frogmen in the Italian Navy with dive watches 80 years ago. A limited-edition Luminor Submersible with a bronze case and a power-reserve display on its dial was unveiled in 2013. Both watches are now available only on the secondary market.
The case of Gérald Genta’s Gefica, launched in 1988, was made of a bronze alloy containing more than 90 percent copper. It is said to be the first bronze luxury watch. Genta supposedly designed the watch at the request of a big-game hunter, who wanted a watch with a matte finish that would not frighten away prey by reflecting sunlight. (Bulgari bought the Gérald Genta brand in 2000 and in 2007 brought out an updated version of the Gefica, also in bronze: the Gefica BiRetro Safari.)
Archimede began making bronze watches in 2013. Like Gérald Genta, it chose the metal for its matte patina, and uses it not only for the cases and crowns but also for the rivets on the leather straps. The watches’ casebacks are steel.
In 2015, Zenith introduced its Pilot Type 20 Extra Special Bronze, which has a 45-mm case. The movement, the Zenith 3000, is automatic. Zenith chose bronze for this version of the watch (it’s also available in steel) because it enhances the watch’s vintage styling.
IWC used bronze for its Aquatimer Chronograph Edition “Expedition Charles Darwin,” introduced in 2014. In that model, IWC’s first bronze watch, the metal is a reference to the HMS Beagle, the ship that took Darwin on his expedition to the Galapagos Islands. Bronze was used for the ship’s portholes, fittings and nautical instruments.
At Baselworld 2016, Tudor introduced the Heritage Black Bay Diver in bronze with an in-house movement. Made from a special alloy of bronze and aluminum, the choice of material is a homage to the use of bronze in historic diving instruments and ships. Featuring a brushed surface, Tudor tell us that the bronze case will develop of a subtle and even patina over time, unique to match its user's habits.
Bronze will never eclipse steel or gold as a watch-case material, but, given the current popularity of dive and nautically themed watches, we’re likely to see more of it in the coming years.